1. Field of the Invention
This invention relates to a substrates bonding method and a substrates bonding device for surface-activated bonding substrates.
2. Description of Related Art
As one of techniques for bonding substrates which are made of varying kinds of materials, a surface-activated bonding technique has been attracting attention. In the surface-activated bonding, substrates are deprived of an impurity by having the surfaces thereof exposed to an inert gas beam in a vacuum. As a result, a state having dangling bonds remain naked (the state having the activated surfaces) is formed on the surfaces of the substrates. Thereafter, the substrates are bonded by causing the surfaces of the substrates to contact each other.
Japanese Patent Application H10-927025A discloses a technique for mutually bonding silicon wafers by irradiating surfaces of silicon wafers with an inert gas ion beam or an inert gas neutral atom beam prior to mutually bonding the silicon wafers thereby removing an impurity from the surfaces of the silicon wafers and effecting mutual bonding of the silicon wafers at normal room temperature.
Since the surface-activated bonding techniques of this principle allow pertinent treatments to be performed at low temperatures as compared with the other substrate bonding techniques such as soldering, they are expected to find application to substrates of varying materials.
The conventional surface-activated bonding techniques are indeed capable of bonding metals and semiconductors by treatments at low temperatures. They, however, are not easily applied to the mutual bonding of substrates whose surfaces are formed of quartz, silicon oxide, silicon nitride, sapphire, LiNbO3, and other ionic crystals. As a result, it has been difficult to accomplish mutual bonding of substrates whose surfaces are made of such materials by a treatment performed at a low temperature.
It has been difficult, for example, to apply the surface-activated bonding technique to a process for mutually bonding quartz substrates with an object of manufacturing an optical device and an optical filter. Also, it has been difficult to apply the surface-activated bonding technique to the manufacture of an electronic device of a new type acquiring a cubic structure by bonding semiconductor substrates provided with electronic circuit containing a metal electrode layer and an insulator layer (silicon oxide or silicon nitride) on the surfaces of the substrates.